1. Technical Field
The present invention relates to a winding method for producing battery electrode groups by winding in a spiral shape both a battery anode (negative electrode) and a battery cathode (positive electrode) superimposed on each other with a separator disposed therebetween as used in lithium secondary batteries, nickel hydrogen batteries and the like, and also relates to a device employing the
2. Background Art
In constructing small and high capacity secondary batteries that are mass-produced, electrode groups formed of such electrode materials as belt-shaped anodes, cathodes, separators and the like superimposed one over another and wound in a spiral shape, respectively, have so far been employed in general. Respective anodes and cathodes are prepared by the steps of filling a paste with an active material serving as the main ingredient in a conductive substrate, drying the paste, performing roll pressing steps for a thickness adjustment of the electrode plates and making the active material layer high in density, cutting the electrode plates to a predetermined width with the used of a slitter to appear belt-shaped and further attaching a lead wire and the like to the respective electrode plates. Separators are formed of a belt-shaped porous polypropylene film and what is generally used are electrode groups, each produced by the steps of having both the foregoing anode and cathode plates superimposed one over another with a predetermined positional relationship maintained and with the separator disposed therebetween, and having the foregoing electrode and separator combination wound around a winding core in a spiral shape tightly without leaving any gaps left between the wound layers.
In producing secondary batteries by the use of electrode groups formed in the foregoing spirally wound body, it is a general practice to produce such spirally wound bodies by putting in place on four unreeling axes that are disposed in parallel with one another the electrode materials of an anode plate, a cathode plate, a first separator and a second separator, all being wound in a roll-shape, respectively. Further, winding cores are provided in parallel to the respective four unreeling axes and the respective tip ends of the electrode materials are tentatively fixed to the winding cores and the respective winding cores are rotated at a constant speed in a predetermined direction.
A tension unit is incorporated in the transportation route of the electrode materials to control a tension applied to thereto so that a tension suitable for winding the electrode groups is applied to each respective electrode material. As the winding core rotates, each respective belt-shaped material constituting the foregoing electrode groups is transported towards the winding core along with the rotation of the unreeling axis and wound around the winding core.
When electrode groups are produced by the use of a winding device as described above, respective anode and cathode plates wound in a roll-shape and fit to an unreeling axis are brought into contact with the periphery of each respective roller that is provided in a plurality for acting as a direction change unit, tension unit and the like and conveyed by running due to the rotation of the rollers. During the foregoing process, irregular end surfaces created on the respective anode and cathode plates in the working steps thereof variations in thickness from place to olace thereof, a localized unlevel condition created in the thickness thereof due to the attachment of lead wires, variations in machining of the electrode plate transporting rollers of the winding device, variations in mounting of the roller axes and the like gradually produce a velocity component perpendicular to the normal running direction thereof, thereby bringing the electrode plates into a meandering movement with the resulting great possibilities of causing a xe2x80x9cstaggered windingxe2x80x9d of the electrode groups.
For reference, a description is given to the case where the width of an electrode material mainly used in a lithium secondary battery is involved. In general, a first separator and a second separator are of the same width and set to around 40 to 60 mm at the maximum of the electrode materials. The width of each respective anode (negative electrode) plate is large after that and the width of the cathode (positive electrode) plate is made the smallest among the electrode materials. Since the difference in width between the separator and the anode plate is about 2 mm and the difference between the anode plate and the cathode plate is about 1 mm, the process of electrode group winding has to be performed carefully so as to have the cathode plate remain within the width of the anode plate that is located opposite to the cathode plate with the separator sandwiched therebetween. In addition, the anode plate is not allowed to extend outside of the width of the separator. Even when the relative positional relationships among the three different electrode materials as described above are satisfied, the respective electrode materials are not allowed to be noticeably displaced in the axial direction of the winding axis as the winding turn to the respective electrode materials increases.
When the foregoing conditions are not satisfied, such defects as battery""s internal short circuits and instability of battery capacity are caused. In the extreme case, it becomes difficult for the electrode groups to be housed in the battery case, resulting in problems not only in the battery""s performance aspect but also the battery""s safety and productivity aspects.
Therefore, a variety of meandering prevention units has been so far employed in the course of electrode materials transportation extending film the unreeling axis to the winding core. Here, some of the equipment is introduced. The most widely used meandering prevention unit is installed at the place where an unreeling axis fit with a roll of each respective electrode material is located. More specifically, the edge position of the electrode material released from the roll is compared with the predetermined reference position and a positional displacement is detected by the use of an optical sensor and the like. Based on the detection result, the unreeling axis fit with the electrode material roll is moved in the direction of the axis core, thereby allowing the edge position of the electrode material to be returned to the predetermined position with an accuracy of 0.1 mm max. This kind of unit is generally for a heavy weight electrode material roll and likely to become large in size and slow in response and, therefore, not suitable for a winding device requiring a high speed and a high degree of accuracy.
According to the Japanese Patent Application Laid-open Publication No. H11-40144, what is characterized by correcting automatically the edge positions of electrode plates is disclosed as FIG. 6 shows. In FIG. 6, there are two axial cores 32a and 33a located perpendicularly to the running direction of respective cathode and anode plates 1 and 3 and the two axial cores are disposed in parallel with each other. An electrode plate is sandwiched between a pair of rollers 32 and 33 held by axial cores 32a and 33a in a rotatable manner, respectively, and the pair of rollers are prepared so as to be allowed to rotate without slippage when the electrode plate is transported. Edge detecting means 34 is disposed in the vicinity of the pair of rollers to detect the edge positions of the electrode plate and, based on the detection results of edge detecting means 34, the pair of rollers are shifted in position in the roller""s axial core direction, thereby correcting the edge positions of the electrode plate automatically.
According to the Japanese Patent Application Laid-open Publication No. H9-120822, a staggered winding prevention unit is disclosed as FIG. 7 shows. In FIG. 7, electrode materials 1 and 3 are cut to a predetermined length to form a rectangular shape, respectively, and the winding end part of each respective rectangular material is gripped in the vicinity thereof by gripping means 29 that is freely movable by sliding in the winding direction along guiding means 28 and, at the same time, cathode plate 1 and anode plate 3 are wound around winding core 7 together with separator 5a via fixing tape while a tension being applied to gripping means 29 in the direction opposing to the winding direction. However, when batteries are produced according to these conventional technologies, there are such problems as a drawback found in the productivity of electrode groups itself, a degraded production yield rate of batteries, an increased variation in quality of batteries and the like.
Further, even at the time of performing an edge control finally, according to the Japanese Patent Application Unexamined publication No. H11-40144, an edge controlling means, whereby an electrode plate is sandwiched between a pair of rollers to correct edge positions, is installed in the vicinity of a winding core, resulting in the possibility of damaging the electrode plate due to an excessive force imposed thereto. Therefore, the edge controlling means is not allowed to be disposed near the winding core, thereby bringing about the danger of staggering edge positions again during the period of time between the time of meandering correction and the time of reaching the winding core as the electrode plate rotates with the roller.
According to the edge control method as disclosed by the Japanese Patent Application Unexamined Publication No. H9-120822, whereby rectangular electrode materials, each being held at the end part thereof by a gripping means that is movable along a guide, are fixed to a separator at the winding start part of respective anode and cathode plates by the use of a fixing tape and then the separator is fit in a slit of the winding core, thereby having the electrode materials wound as the winding core is rotated, staggered winding hardly occurs and the accuracy of staggered winding observed with electrode groups is expected to be excellent. However, in what way the end part of the respective sheet-like electrode materials is fed to the gripping means automatically and efficiently and gripped thereby is not disclosed and it is not expected that sufficient productivity can be realized. Also, the use of a fixing tape that is irrelevant to the performance of batteries makes this method present problems in terms of performance and costs.
Conventional winding core 7 is circular in cross section as FIG. 8 (a) shows and, when the cylindrically wound electrode group as shown in FIG. 8 (b) is flattened in shape by applying a pressing force thereto, the positions, where the electrode group is bent, are not fixed, thereby presenting the problem of not allowing the positions, where lead wires of the electrodes are taken out, to be fixed. In addition, the cross-section of the electrode group looks like a cocoon as FIG. 8 (c) shows, thereby causing an adverse effect to the flatness of the electrode group when it comes to the flat shaping thereof.
Recently, as disclosed in the Japanese Patent Application Unexamined Publication No. H6-96801, a flat winding core shaped like a rectangle in cross section has been employed in winding electrode groups. FIG. 9 (a) shows a typical flat-shaped winding core. FIG. 9 (b) an FIG. 9 (c) are cross-sectional views of an electrode group formed by winding around the winding core and another electrode group shaped flatly with a pressing force applied thereto, respectively. It this case, the volumetric efficiency of the electrode groups in the battery case is excellent but there are such problems as staggered windings likely to be caused by pulsation in the peripheral speed of winding around the winding core, difficulties in having the winding core shaped flat in cross section taken out of the wound electrode group, poor retainability of electrolyte because of lack of leeway in separator and space, and the like.
In order to solve the problems as described above, the present invention discloses an electrode group winding method whereby, when long belt-like electrode materials are would to form an electrode group, an electrode group with an extremely small amount of staggered windings realized by correcting efficiently and accurately the shifts in position created on a variety of electrode materials such as cathode plate 1, anode plate 3 and the like in the direction of transportation hereof and also in the direction perpendicular thereto is allowed to be produced continuously without cutting the electrode materials to a rectangle-shape and also with excellent flatness, and provides a device utilizing the method and batteries with stabilized quality and excellent productivity.
A spiral electrode group winding method based on the present invention comprises the steps of:
fitting long belt-like electrode materials such as an anode plate, a cathode plate and a separator to an unreeling axis, respectively;
transporting the electrode materials towards respective winding cores while the transportation directions are changed via a meandering prevention unit, a tension unit and a plurality of electrode materials transportation rollers that are put in place on the transportation route extending from the unreeling axis to the winding core to take up the electrode materials, respectively;
detecting edge positions of respective belt-like electrode materials, particular of the anode and cathode plates, at a predetermined position in the vicinity of the winding core but the use of an edge detecting means to compare the detected edge positions with the reference portion; and
correcting the positional shifting of the edges of electrode plates in the direction perpendicular to the transportation direction of the electrode plates based on the detection results by the use of a chuck driving means formed of a servomotor and a ball screw after the electrode plate is gripped by a pair of fingers of a chuck extending from the end part of the electrode plate id the direction perpendicular to the running direction of the electrode plate.
Once the edge position of an electrode plate is automatically corrected with a sufficient degree of accuray, the distal end pan of the electrode plate extending over the length needed to finish one winding of spiral electrode group is gripped by a second chuck, the shifting of which is restricted to a direction parallel to the transportation direction of the electrode plate by means of a guide disposed in parallel to the transportation direction of the electrode materials to prevent the positional shifting in the direction perpendicular to the running direction of the electrode plate, and further the electrode plate is gripped by a third chuck, which is restricted in the movement thereof in the direction parallel with the transportation direction of the electrode plate, at the distal end part of the electrode plate extending over the length needed to finish one winding of spiral electrode group and the tip end part of the electrode plate is fed to the winding core in such a way as to not cause a shift in position, thereby preventing a positional shift from taking place by an action of the second chuck and also performing the electrode group winding while a tension is applied thereto.
Also, the spiral electrode group winding method is characterized by producing spiral electrode groups continuously for the enhancement of productivity of the electrode groups without cutting the anode and cathode plates to a rectangular shape, respectively, by operating in a sequentially orderly manner the cutter for electrode cutting and the cutter for separator cutting installed near the winding core.
A spiral electrode group winding device of the present invention comprises:
an unreeling axis fit with a long belt-shaped electrode material; and
a meandering prevention unit, a tension unit and a plurality of electrode material transporting rollers to transport the electrode materials towards a winding core while the direction of transportation is changed, which are disposed on the transportation route extending from the unreeling axis to the winding core to take the electrode materials, comprises:
an edge position detecting unit for detecting edge positions of an electrode plate disposed on each respective transportation route of both anode and cathode plates in the vicinity of a predetermined position of the winding core to correct finally the edge positions of the anode and cathode plates; and
an edge position correcting chuck structured so as to be put in motion by a pair of fingers extending in the direction perpendicular to the running direction of the electrode plate, a servomotor and a ball screw, thereby correcting the edge positions by comparing with the reference position.
The spiral electrode group winding device is characterized by disposing a second chuck for winding the electrode groups while a tension is applied thereto with the electrode plate restricted in movement only in the direction parallel to the transportation direction of the electrode late by means of a guide after the edge positions of the electrode plate is corrected with a sufficient degree of accuracy in order to prevent a positional shift of the electrode plate in the direction perpendicular to the running direction thereof, and by disposing a third chuck to feed the tip end part of the electrode plate to the winding core under the condition where no positional shift of the electrode plate is taking place and disposing an electrode plate cutter between the third chuck and the winding core, thereby allowing the electrode plate to be cut at an immediate position before the winding core.
Batteries having the spiral electrode groups of the present invention built therein are characterized by being stabilized in quality and excellent in productivity.